The numerical control system is the position control system, which has 3 basic functions. 1. input function: refers to the parts processing program and input of various parameters. 2. interpolation function: means of determining some intermediate points between the known points of the actual parts or tracks of the machined parts. The middle point is usually interpolated between the starting point and the end point of a given line or arc. The interpolation methods include pulse increment method and digital increment method. The former is characterized by the generation of a feed pulse in each interpolation operation. The maximum rate of the output pulse depends on the time required to perform an interpolation grate. This method is suitable for the open loop CNC system driven by the stepper motor, and the feed rate is low. The characteristics of the latter are as follows: the whole control system forms a closed loop through the computer, and the grating machine is used to feed and feed back the actual position regularly. The sampling results are compared with the instruction data generated by the interpolation, and the error signals are obtained. Then the spindle feed speed instruction is given. This method is suitable for the position sampling control of the direct and AC servo motor. System system.